Geochronology, geochemistry, and geological significance of early Jurassic intrusive rocks in the Lesser Xing’an- Zhangguangcai Range, northeast China

The Lesser Xing’an—Zhangguangcai Range of northeast China is located in the eastern segment of the Central Asian Orogenic Belt (CAOB), which records intense magmatism during the Mesozoic. The petrogenesis and geodynamic setting of the Early Jurassic intrusive rocks in this region are unclear. In this paper, we present new zircon U–Pb age and whole-rock geochemical data for these intrusive rocks to investigate their origins and tectonic setting. Zircon U–Pb dating suggests these intrusive rocks were emplaced during the Early Jurassic (197–187 Ma). The granites are enriched in silica and alkali, and depleted in MgO and CaO. They are metaluminous to weakly peraluminous, and have high A/CNK values and low zircon saturation temperatures (TZr ~ 779°C), suggesting they are highly fractionated I-type granites derived by partial melting of lower crustal materials. The granites exhibit negative Nb, Ta, P, Eu, and Ti anomalies due to fractional crystallization. The diorites and gabbros have low SiO2 contents and high Mg# values, and are enriched in light rare earth and large-ion lithophile (Ba, K, and Sr) elements, and depleted in heavy rare earth and high field strength (Nb, Ta, and Ti) elements. The geochemical characteristics show that the mafic magmas were derived by partial melting of mantle that had been metasomatized by subduction-related fluids. Based on the geochemical characteristics of coeval intrusive rocks and the regional geological setting, we suggest the Early Jurassic intrusive rocks in the Lesser Xing’an—Zhangguangcai Range were formed along an active continental margin, possibly as a result of bidirectional subduction of the Mudanjiang Oceanic plate between the Jiamusi and Songnen—Zhangguangcai Range massifs.


Introduction
The Lesser Xing'an-Zhangguangcai Range in northeast (NE) China is located between the Jiamusi and Songnen massifs, and contains abundant Late Paleozoic to Mesozoic igneous

Geological background
NE China is located between the North China Plate and the Siberian Plate, in the easternmost CAOB (Fig 1a [32]).It formed by complex tectonic and magmatic processes involving microcontinental plates, including the Ergun, Xing'an, Songliao, and Jiamusi massifs, and Nadanhada Terrane (from west to east) [14,27,[32][33][34][35] (Fig 1b [14]).The study area is located in the Lesser Xing'an-Zhangguangcai Range, near the suture zone between the Jiamusi and Songnen-Zhangguangcai Range massifs, with the Jiamusi and Jiayin-Mudanjiang massifs to the east and Songnen Massif to the west.
The strata in the study area comprise the Lower Permian-Lower Triassic Hongguang Formation of the Zhangguangcai Range Group and Cenozoic-Quaternary rocks.The Hongguang Formation is distributed in a NE-SW to nearly N-S direction, and was intruded by Early Jurassic syenogranites, monzogranites, and granodiorites.The Hongguang Formation consists mainly of gray-black migmatites and intermediate-acidic volcanic rocks intercalated with marbles.The Quaternary strata are mostly distributed in linear bands along terraces and valleys on both sides of major rivers, and consist of clay and unconsolidated gravel.
The geological setting of the study area is complex and includes Late Archean-Mesoproterozoic continental breakup, Late Proterozoic-Early Paleozoic oceanic basin formation, Early Paleozoic convergence of the North China and Siberian plates (and other microplates) [36,37], Late Paleozoic subduction and closure of the Paleo-Asian Ocean, collision of the southern margin of the Siberian Plate and northern margin of the North China Plate [38,39], and westward subduction of the Pacific Plate and evolution of the Mongol-Okhotsk tectonic domain [19,20,40].The study area contains abundant igneous rocks in a N-S-trending and sporadic upper Paleozoic strata [41] (Fig 1c [10,14]).These igneous rocks are diverse and include acid, intermediate, and (ultra)mafic rocks, with granites being particularly common.

Petrography
Early Jurassic intrusive rocks are widely distributed in the study area.Acid intrusive rocks are common and intermediate-mafic intrusive rocks are sporadically exposed, including syenogranite, monzogranite, diorite, and gabbro (Fig 2).To constrain the tectonic evolution of the Lesser Xing'an-Zhangguangcai Range, we sampled syenogranites, monzogranites, granodiorites, diorites, and gabbros.
The diorite (TW04) occurs in the form of a stock.The Early Jurassic diorite intruded a gabbro, and was intruded in turn by granodiorite and monzogranite.The sample is gray-black in color, with a fine-grained granular texture and massive structure (Fig 3j).It consists of plagioclase (70 vol.%), amphibole (20 vol.%), biotite (7 vol.%), and quartz (3 vol.%), with accessory magnetite and zircon.

Zircon U-Pb dating
The zircon grains were separated in the laboratory of the Langfang Fengzeyuan Rock and Ore Detection Technology Company, China.After mechanical crushing, and heavy liquid and magnetic separation, we handpicked relatively complete and transparent zircon grains under a binocular microscope.Zircons were mounted in epoxy resin and polished to expose their centres for cathodoluminescence (CL) imaging at the Beijing Createch Testing Technology Company, China.The zircons were dated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS).The data processing was undertaken with ICP-MS Data Cal software.The standard zircon 91500 was used as the external standard, and the standard zircon GJ-1 was used for monitoring data quality.NIST 610 were used as an external standard to calibrate zircon trace element contents, and 29 Si was used as an internal standard.Common Pb was corrected following Andersen (2002) [42].The U-Pb age calculations and concordia plots were obtained with Isoplot 3.0.The concordia ages are quoted at the 95% confidence level and the dating results are presented in Table 1.

Whole-rock major and trace element analyses
We sampled representative intrusive rocks from outcrops and trenches in the study area for geochemical analysis.Major and trace element analysis was carried out at the Geological Research and Testing Center of First Geological Exploration institute of Heilongjiang Province, China.Fresh rock samples were washed with distilled water and air-dried.The samples were then dried in an oven at 120˚C and powdered to 200 mesh with an agate mortar and pestle.Major and trace elements were determined by X-ray fluorescence (XRF) spectrometry with   an accuracy of <3%.Trace elements were determined by ICP-MS.The major and trace element data are listed in Table 2.
The syenogranite was collected from the Yingzuilazi-Diaoshuihu pluton.A total of 20 zircon U-Pb ages were selected and tested, and one discordant age was eliminated.The 206 Pb/ 238 U ages given by 19 zircon grains range from 188 to 197 Ma, and yielded the weighted mean 206 Pb/ 238 U age of 192±2.4Ma (MSWD = 0.3) (Fig 4b).This indicates the syenogranite was formed in Early Jurassic.
The monzogranite was sampled both sides of south-central Laoyeling highland and the northern part area around the Jiaxinshan-Weixing section.A total of 20 zircon U-Pb ages were selected and tested, excluding one discordant age.The 206 Pb/ 238 U ages given by 19 zircon grains range from 183 to 193 Ma, and yielded the weighted mean 206 Pb/ 238 U age of 187±1.6Ma (MSWD = 0.81) (Fig 4d).This indicates that the formation age of monzogranite is Early Jurassic.
The granodiorite was collected from the southern pluton of Shuguang forest farm.The zircon grains are small, ranging from 90 to 100 μm, and most of the zircon grains are 90 μm.A total of 20 zircon U-Pb ages were selected and tested, and one discordant age was eliminated.The 206 Pb/ 238 U ages given by 19 zircon grains range from 190 to 197 Ma, and the weighted mean 206 Pb/ 238 U age was 194±2.8Ma (MSWD = 0.043) (Fig 4f).This suggests that the formation age of granodiorite is Early Jurassic.
The diorite was taken from the 945 highland-698 highland pluton in the north of Laoyeling.The zircon grains are large, ranging from 100 to 130 μm.Most of the zircon grains are 100 μm, and the large ones can reach more than 150 μm.A total of 20 zircon U-Pb ages were selected and tested, and 3 discordant ages were removed.The 206 Pb/ 238 U ages given by 17 zircon grains

Ages of the intrusive rocks from the Lesser Xing'an-Zhangguangcai Range
In recent years, previous studies have carried out on magmatism, plate amalgamation, tectonic setting in the Lesser Xing'an-Zhangguangcai Range.Moreover, they have conducted extensive research on the formation age and petrogenetic types of rocks [9-12, 19-26, 28-30].Some studies consider that the formation ages of the granites in the Lesser Xing'an-Zhangguangcai Range were mainly in the Mesozoic-Late Paleozoic, with the most intense magmatic activity occurring from Late Triassic to Early Jurassic [10][11][12][19][20][21][22][23][24].Only minor granites were formed in the Neoproterozoic and Early Paleozoic [13,14,29,30].Other studies have proposed that the mafic-ultramafic intrusive rocks exposed in Shuguang forest farm, Liuzhonggou, Xincun, Pingfang and Yichun areas of the Lesser Xing'an-Zhangguangcai Range and the diabase in Tieli area [9,25,31].These studies show that the mafic-ultramafic rocks are formed in the Early Jurassic.In recent years, previous have carried out abundant zircon U-Pb dating studies on the pluton in the Lesser Xing'an-Zhangguangcai Range.And the Early Paleozoic pluton is corrected to late Paleozoic and Mesozoic [27,51].In this paper, we conducted zircon U-Pb dating on five types of intrusive rocks in the study area.The ages of intrusive rocks are 197-187 Ma.In summary, this is consistent with the previous geological study results.
The spatiotemporal distribution pattern of intrusive rocks in the Lesser Xing'an-Zhangguangcai Range is of significance to explore the tectonic setting of the region.Ge et al.(2020b) collected formation ages of Late Paleozoic-Mesozoic granites, showing a spatiotemporal characteristic of gradually becoming juvenile from east to west [26].In this paper, we not only collects the age of granites, but also adds the age of intermediate-mafic intrusive rocks (Table 3).Due to this area is located near the Jiamusi-Yilan fault of the northern section of the Tanlu fault.In order to eliminate the influence of strike-slip displacement caused by the Jiamusi-Yilan fault, the age data are divided into two groups based on the north and south sides of the fault to plot diagrams (Fig 8a -8c).We find that the Late Paleozoic-Mesozoic intrusive rocks gradually become juvenile from east to west.

Petrogenesis
Petrogenesis and magmatic evolution of the granites.The types of granitoids include syenogranite, monzogranite, and granodiorite.They consist mainly of quartz, plagioclase, Kfeldspar, and amphibole, along with accessory apatite, zircon, magnetite, and titanite.The granitoids do not contain minerals characteristic of typical S-type granites, such as muscovite, garnet, and cordierite [71].The samples are metaluminous to weakly peraluminous, with A/ CNK < 1.1.These geochemical characteristics are distinct from those of S-type granites [72,73].All samples plot in the I-type granite field in an AFM diagram (Fig 9d).However, highly fractionated I-and A-type granites can exhibit similar mineralogical and geochemical features [72].
Alkaline mafic minerals (riebeckite-arfvedsonite and aegirine-augite) and Fe-rich olivine (fayalite) are usually important mineralogical indicators of A-type granites [19,26].The studied granites contain alkali feldspar, quartz, plagioclase, and minor biotite and amphibole, but do not include alkaline mafic minerals.The mineralogy is typical of highly fractionated I-type granites.The granite samples plot in the I-type granite field in FeO T /MgO-(Zr + Nb + Ce + Y), Zr-10000Ga/Al, and Ce-SiO 2 diagrams (Fig 9a -9c).Furthermore, the low zircon saturation temperature (T zr = ~779˚C) of the samples differs from those of A-type granites (>800˚C) (Table 2), but is consistent with those of highly fractionated I-type granites.I-type granites can form by: (1) fractional crystallization of mantle-derived mafic magmas [77]; (2) partial melting of lower crustal material [78]; or (3) mixing of mantle-and crustalderived magmasl [79].The studied granitoids are characterized by high silica and alkali contents, and low MgO and CaO contents.They are metaluminous to peraluminous, high-K calcalkaline rocks, with relatively low Mg # values.These features indicate the granitic magmas were derived from the crust.The granites have relatively high SiO 2 contents and A/CNK values, and negative anomalies in Nb, Ta, P, Eu, and Ti, indicating the magmas experienced fractional crystallization [80,81].In Harker diagrams (Fig 10), TiO 2 , Al 2 O 3 , MnO, CaO, and Mg # decrease with increasing SiO 2 , whereas K 2 O increases.These features are consistent with fractional crystallization of biotite, plagioclase, amphibole, titanite, and apatite.The Eu anomalies are due to fractional crystallization of K-feldspar and plagioclase.The P depletion is due to fractional crystallization of apatite, and the Ti depletion was caused by fractional crystallization of minerals such as ilmenite and titanite.These inferred fractionating phases are consistent with the petrography.
Petrogenesis and magmatic evolution of the diorites.Previous studies have proposed three models for the formation of diorites: (1) melting of mafic lower crust [82]; (2) fractional crystallization of mantle-derived magma [83]; and (3) partial melting of mantle metasomatized by subduction-related components [84,85]  V, Ni, Co, and Cr.The average Ti/Zr ratio is 36.5, which is inconsistent with the Ti/Zr ratio of crust-derived magmas (Ti/Zr < 30).The Nb/Ta ratios are 16.24-19.05,with an average of 17.17, similar to the mantle average of 17.5 [50].The samples plot in the subduction-metasomatized lithospheric mantle field on a La/Ba-La/Nb diagram (Fig 12d).Therefore, the source of the diorites was mantle that had been metasomatized by subduction components.
Mantle-derived magmas can be contaminated by crust during magma ascent.In general, there is a significant linear relationship between Ce/Pb or Nb/La ratios and SiO 2 contents when diorites experience crustal contamination [88].However, the studied diorites lack this linear relationship (Fig 12a and 12b).In addition, the diorites have no obvious positive Zr anomalies.In a Ba/Nb-La/Nb diagram (Fig 12c), the samples plot in the arc volcanic field and not between the crust and mantle fields, which precludes the possibility of significant crustal  [76]) (The reference data come from [1,22,26,31,47,48]). contamination.If the mantle source had been metasomatized by subduction zone melts, it would be relatively enriched in Th and light rare earth elements (LREEs; Th/Yb � 2).However, the Th/Yb ratios of the diorites in the study area are 0.97-1.54,indicating the dioritic magma was not derived from a source that had been metasomatized by sediment-derived melt [89,90].In addition, in Th/Yb-Ba/La and Nb/Y-La/Yb diagrams (Fig 13a and 13b) the diorite samples plot in the field of fluid metasomatism, indicating the dioritic magma was derived from a source that had been metasomatized by fluids generated by dehydration of a subducted oceanic plate.
Petrogenesis and magmatic evolution of the gabbros.The studied gabbros consist of pyroxene, plagioclase, amphibole, and olivine, and the amphibole is altered, which may have affected the geochemistry.The element Zr is used to assess the mobility of other elements because of its immobile characteristics [95][96][97].There is a positive correlation between Zr and Th, Sm, La, Nb, Ti, and Ta contents, indicating these elements were not affected by alteration (Fig 14) [98].The gabbros have low SiO 2 contents, high Mg # values, and high TiO 2 contents, indicating they were derived by partial melting of the mantle [99,100].Mantle-derived magmas are susceptible to crustal contamination during magma ascent [101].The continental crust is strongly depleted in Nb, Ta, and Ti [50,102].If the magma undergoes crustal contamination, it will develop island arc-like or crust-like geochemical properties [103].The studied gabbros are characterized by enrichments in large-ion lithophile elements (LILEs; Ba and K) and depletions in high-field-strength elements (HFSEs; Ta and Ti), indicative of mantle-derived magma contaminated by continental crust.However, other evidence suggests that the mantle-derived magmas were not contaminated by the crust.Despite the relative enrichment of Zr and Hf in the continental crust, Zr in the studied samples does not exhibit obvious positive anomalies in primitive mantle-normalized trace element diagrams (Fig 7d).In addition, compared with the continental crust, the gabbros have lower Th/Ce (0.02-0.06),Th/La (0.04-0.14), and Th/Yb (0.27-0.74) ratios, and higher Nb/Th (2.56-4.45)ratios.These results indicate the mafic magmas might not contaminated by the crust.Therefore, the parental magmas of the gabbros in the Shuguang Forest Farm area were not obviously contaminated by the crust during magma ascent.As such, the negative Ta and Nb anomalies reflect those of the mantle source.The gabbros is enriched in LREEs and LILEs, and depleted in HREEs and HFSEs, and it can be inferred that the gabbroic magma was derived from a mantle source that had been metasomatized by subduction-related fluids or melts [104][105][106][107][108][109].Previous studies have shown that fluid derived from a subducted slab is enriched in Ba, Rb, U, and Pb, and depleted in LREEs, Th, and HFSEs (e.g., Zr, Nb, and Ta) [110,111].The melts produced by partial melting of subducted sediments are enriched in LREEs, Th, Rb, Ba, U, Sr, and Pb [112] The REE contents and ratios can be used to infer the origins and degree of melting of mantle-derived magmas [94,113].The Sm/Yb ratio can be used to identify the mineralogy of the mantle source [94].In La/Ba-La/Nb (Fig 13c ) and Sm/Yb-Sm diagrams (Fig 13d), the samples plot in the subduction metasomatized lithospheric mantle field and near the partial melting trend for spinel-garnet (1:1) lherzolite.This indicates the mantle source was spinel-garnet lherzolite, and the degree of partial melting was 10%-20%.

Tectonic implications
The Lesser Xing'an-Zhangguangcai Range is located between the Jiamusi and Songnen massifs, and contains Late Paleozoic-Mesozoic igneous rocks.Most of these rocks are part of the  The Lesser Xing'an-Zhangguangcai Range was located in an active continental margin environment during the Jurassic, and the magma source was modified by subduction-related fluid derived from oceanic lithosphere [1,9,121,122].Previous studies of Early-Middle Triassic collisional granites from the southern margin of the Xingmeng Orogenic Belt have concluded that the Paleo-Asian Ocean closed in the Early-Middle Triassic.Late Triassic bimodal igneous rocks in the Zhangguangcai Range suggest the region was in an extensional setting during this period, which also indicates the Paleo-Asian Ocean closed before the Late Triassic [3,31,123,124].Therefore, the tectonic setting in the Early Jurassic was not related to Paleo- Asian Ocean.The 'Mudanjiang Ocean' refer to an ancient ocean between the Jiamusi and Songnen-Zhangguangcai Range massifs [14].The Mudanjiang Ocean may have been the dominant factor in the Mesozoic tectonic evolution of this region.Therefore, the tectonic evolution of the Mudanjiang Ocean is of significance in understanding the tectonic history of these two massifs.The timing and polarity of subduction in the Mudanjiang Ocean are controversial.Liu et al.(2019) determined the age of an ophiolitic melange in northeast China, and concluded that the Mudanjiang Ocean existed from the Late Permian to Middle Jurassic [15].Based on a study of the Heilongjiang Complex and detrital zircon geochronology, Sun et al. (2018) and Xu et al.(2019) suggested that the Mudanjiang Ocean existed during the Middle Triassic-Early Jurassic [17,125].Based on the ages of blueschists and plagioclase amphibolites with ocean island basalts (OIB) and mid ridge island basalts (MORB), Dong Y.(2018a) proposed that the Mudanjiang Ocean existed during the Late Paleozoic-Early Jurassic [12].Given the temporal and spatial distribution of arc magmatism, as well as its petrogenesis, it is inferred that the subduction polarity in the Mudanjiang Ocean was mainly westward [11,16] and/or bidirectional [12,13,18].
Based on the temporal and spatial distribution, petrogenesis, and tectonic setting of igneous rocks in the Lesser Xing'an-Zhangguangcai Range on the eastern margin of the Songnen and Jiamusi massifs, we consider that the Mudanjiang Ocean existed from the Early Permian to Middle Jurassic, and the subduction polarity was bidirectional (Fig 18 Heilongjiang Complex formed at an active continental margin [126], indicating the Mudanjiang Ocean had opened and was experiencing subduction at this time.The Permian igneous rocks along the western margin of the Jiamusi Massif and eastern margin of the Songnen Massif are bimodal [6,13,127], indicating an extensional environment.The N-Strending Permian granite belt located along the eastern margin of the Songnen-Zhangguangcai Range Massif (Permian arc-related igneous rocks are distributed in the Lesser Xing'an-Zhangguangcai Range, including the Zhushan [12], Hengtoushan [12], and Huangqigou areas [70]), indicates the Mudanjiang Ocean experienced westward subduction.A N-S-trending belt of Permian granite occurs to the east and west of the Jiamusi Massif.However, Permian arc-related igneous rocks in the eastern Jiamusi Massif (302-260 Ma) [128][129][130][131][132] were formed earlier than Permian arc-related igneous rocks in the western Jiamusi Massif (296-246 Ma) [29,51,133,134], indicating the latter were formed by eastward subduction in the Mudanjiang Ocean.
2. Before 180 Ma, the Mudanjiang Ocean continued to experience bidirectional subduction, and the oceanic basin decreased in size.Triassic and Early Jurassic arc-related igneous rocks along the eastern margin of the Songnen-Zhangguangcai Range indicate the Mudanjiang Ocean experienced westward subduction (e.g., in the Taiqing [14], Lianzhushan [63], Tianqiaogang [62], Xingfulinchang [19] and Shuguang Forest Farm areas).3. Before 160 Ma, the Mudanjiang Ocean continued to undergo bidirectional subduction and finally closed.The metamorphic ages of the Heilongjiang Complex can constrain the timing of closure of the Mudanjiang Ocean.Phengite 40 Ar/ 39 Ar ages (186-165 Ma) of metasedimentary and blueschist-facies rocks in the Heilongjiang Complex are younger than [17,31,135], and partly overlap, those of metamorphic zircon and arc-related igneous rocks in the Zhangguangcai Range, suggesting the phengite 40 Ar/ 39 Ar ages record the long-term tectonic exhumation of high-pressure metamorphic rocks due to subduction of the Mudanjiang oceanic lithosphere and collision between the Jiamusi and Songnen massifs.2. The Early Jurassic granites in the study area are highly fractionated I-type granites derived by partial melting of the lower crust, which underwent biotite, plagioclase, amphibole, and titanite fractionation crystallization.The dioritic and gabbroic magmas were derived by partial melting of a mantle source that had been metasomatized by subduction-related fluids and did not undergo obvious crustal contamination.The gabbros underwent fractional crystallization of pyroxene, and the diorites experienced fractional crystallization of amphibole.
3. The Early Jurassic intrusive rocks have arc-like geochemical characteristics, similar to igneous rocks formed in a subduction setting along the eastern margin of the Songnen-Zhangguangcai Range Massif.This indicates they formed in an active continental margin environment, perhaps related to bidirectional subduction in the Mudanjiang Ocean during the Early Jurassic.

Fig 1 .
Fig 1.(a) Regional map showing the location of Central Asian Orogenic Belt; (b) Tectonic divisions sketch map of NE China; (c) Distribution of magmatic rocks in the Lesser Xing'an-Zhangguangcai Range.The original basemap was obtained from Natural Earth (http://www.naturalearthdata.com/) and was further processed using software ArcGIS 10.8 version.Digital elevation model was from the USGS National Map Viewer (http://viewer.nationalmap.gov/viewer/).https://doi.org/10.1371/journal.pone.0306465.g001

Fig 7 .
Fig 7. Chondrite-normalized REE patterns and primitive-mantle-normalized trace element diagrams of intrusive rocks in the study area (chondrite and primitive mantle values are from [50]) (the data source of the shadow part is consistent with Fig 6).https://doi.org/10.1371/journal.pone.0306465.g007 . The magmas produced by melting of mafic lower crust typically have Mg # values of <40.Diorites formed by fractional crystallization of mantlederived magmas generally have high Mg # values (>60) and low TiO 2 contents (<0.5 wt.%) [86].However, the studied diorites have low Mg # values (42-47) and high TiO 2 contents (0.70-0.94 wt.%).In Harker diagrams (Fig 10), TiO 2 , FeO T , MnO, MgO, and Mg # are negatively correlated with SiO 2 contents, indicating the diorites underwent fractional crystallization of amphibole and plagioclase.The samples also define a partial melting trend in a La/Yb-La diagram (Fig 11a), which is not consistent with fractional crystallization.Most of the diorite samples do not plot in the crust source field in a (La/Yb) N -δEu diagram (Fig 11b), indicating the magmas were not derived from the lower crust.Therefore, the diorites were not derived from the mafic lower crust or by fractional crystallization of mantle-derived magma.The diorites have low SiO 2 and high MgO contents, and are enriched in transition elements, such as

). 1 .
During 288-250 Ma, the Mudanjiang Ocean had already opened and was undergoing bidirectional subduction.Ge et al.(2017, 2018) obtained the protolith ages of blueschists in the Early Permian Heilongjiang Complex in Yilan (tholeiitic series = 288 ± 2 Ma; alkaline series = 288 ± 2 Ma) and showed it had OIB-like features [10, 11], indicating the Mudanjiang Ocean between the Jiamusi and Songnen massifs was open by at least the Early Permian.Dong et al.(2018b) proposed that the Early Permian Yilan amphibolites (274 Ma) in the There are no Early-Middle Triassic ophiolites or arc igneous rocks along the eastern margin of the Jiamusi Massif, and only Early Triassic (250-246 Ma) I-type granites occur in the Fuxing Forest Farm and Diaoling Town areas of Linkou County along the western margin of the Jiamusi Massif [51], indicating eastward subduction in the Mudanjiang Ocean.The Early Jurassic (197-187 Ma) intrusive rocks in the Shuguang Forest Farm area of the Lesser Xing'an-Zhangguangcai Range formed along an active continental margin, indicating the Mudanjiang Ocean was experiencing subduction at this time.Late Mesozoic-Paleogene intrusive rocks in the Lesser Xing'an-Zhangguangcai Range gradually young from east to west, which also shows that subduction in the Mudanjiang Ocean occurred during the Mesozoic-Paleogene.The Lesser Xing'an-Zhangguangcai Range contains abundant late Paleozoic and Mesozoic igneous rocks that are medium-to high-K calc-alkaline in composition.They are enriched in LREEs and LILEs, and depleted in HREEs and HFSEs, and have arc-like geochemical properties, suggesting the Mudanjiang Ocean was undergoing subduction during this period.